I've run in the exceptions a few times when doing
'git cl presubmit' or 'git cl lint' from a detached
HEAD state (not uncommon when using 'git rebase-update')

Review URL: https://codereview.chromium.org/792933003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@293643 0039d316-1c4b-4281-b951-d872f2087c98